Organic electroluminescent materials and devices

ABSTRACT

A compound of the formula MLALB where ligand LA is of Formula I, and ligand LB is of Formula II below.M is selected from Os(II) or Ru(II), and the compound MLALB has a formal neutral charge; and rings A, B, C, D, E, and F are independently a 5-membered or 6-membered aromatic ring, and RA, RB, RC, RD, RE,and RF each independently represent mono to the maximum allowable substitution, or no substitution.L1, L2, L3, and L4 independently represent a single bond or an organic linking group;W1, W2, W3, and W4 are independently selected from carbon or nitrogen;Y1, Y2, Y3, and Y4 are independently selected from carbon or nitrogen; andZ1, Z2, and Z3 are independently selected from carbon or nitrogen, and at least one of Z1, Z2, and Z3 is nitrogen. An organic electroluminescent device that includes an anode, a cathode, and an organic layer comprising a compound of the formula MLALB where ligand LA is of Formula I, and ligand LB is of Formula II above. A consumer product comprising an organic light-emitting device (OLED) above.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Application No. 62/598,571, filed Dec. 14, 2017, the entire contents of which are incorporated herein by reference.

FIELD

The present invention relates to compounds for use as emitters, and devices, such as organic light emitting diodes, including the same.

BACKGROUND

Opto-electronic devices that make use of organic materials are becoming increasingly desirable for a number of reasons. Many of the materials used to make such devices are relatively inexpensive, so organic opto-electronic devices have the potential for cost advantages over inorganic devices. In addition, the inherent properties of organic materials, such as their flexibility, may make them well suited for particular applications such as fabrication on a flexible substrate. Examples of organic opto-electronic devices include organic light emitting diodes/devices (OLEDs), organic phototransistors, organic photovoltaic cells, and organic photodetectors. For OLEDs, the organic materials may have performance advantages over conventional materials. For example, the wavelength at which an organic emissive layer emits light may generally be readily tuned with appropriate dopants.

OLEDs make use of thin organic films that emit light when voltage is applied across the device. OLEDs are becoming an increasingly interesting technology for use in applications such as flat panel displays, illumination, and backlighting. Several OLED materials and configurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and 5,707,745, which are incorporated herein by reference in their entirety.

One application for phosphorescent emissive molecules is a full color display. Industry standards for such a display call for pixels adapted to emit particular colors, referred to as “saturated” colors. In particular, these standards call for saturated red, green, and blue pixels. Alternatively the OLED can be designed to emit white light. In conventional liquid crystal displays emission from a white backlight is filtered using absorption filters to produce red, green and blue emission. The same technique can also be used with OLEDs. The white OLED can be either a single EML device or a stack structure. Color may be measured using CIE coordinates, which are well known to the art.

One example of a green emissive molecule is tris(2-phenylpyridine) iridium, denoted Ir(ppy)₃, which has the following structure:

As used herein, the term “organic” includes polymeric materials as well as small molecule organic materials that may be used to fabricate organic opto-electronic devices. “Small molecule” refers to any organic material that is not a polymer, and “small molecules” may actually be quite large. Small molecules may include repeat units in some circumstances. For example, using a long chain alkyl group as a substituent does not remove a molecule from the “small molecule” class. Small molecules may also be incorporated into polymers, for example as a pendent group on a polymer backbone or as a part of the backbone. Small molecules may also serve as the core moiety of a dendrimer, which consists of a series of chemical shells built on the core moiety. The core moiety of a dendrimer may be a fluorescent or phosphorescent small molecule emitter. A dendrimer may be a “small molecule,” and it is believed that all dendrimers currently used in the field of OLEDs are small molecules.

As used herein, “top” means furthest away from the substrate, while “bottom” means closest to the substrate. Where a first layer is described as “disposed over” a second layer, the first layer is disposed further away from substrate. There may be other layers between the first and second layer, unless it is specified that the first layer is “in contact with” the second layer. For example, a cathode may be described as “disposed over” an anode, even though there are various organic layers in between.

As used herein, “solution processable” means capable of being dissolved, dispersed, or transported in and/or deposited from a liquid medium, either in solution or suspension form.

A ligand may be referred to as “photoactive” when it is believed that the ligand directly contributes to the photoactive properties of an emissive material. A ligand may be referred to as “ancillary” when it is believed that the ligand does not contribute to the photoactive properties of an emissive material, although an ancillary ligand may alter the properties of a photoactive ligand.

As used herein, and as would be generally understood by one skilled in the art, a first “Highest Occupied Molecular Orbital” (HOMO) or “Lowest Unoccupied Molecular Orbital” (LUMO) energy level is “greater than” or “higher than” a second HOMO or LUMO energy level if the first energy level is closer to the vacuum energy level. Since ionization potentials (IP) are measured as a negative energy relative to a vacuum level, a higher HOMO energy level corresponds to an IP having a smaller absolute value (an IP that is less negative). Similarly, a higher LUMO energy level corresponds to an electron affinity (EA) having a smaller absolute value (an EA that is less negative). On a conventional energy level diagram, with the vacuum level at the top, the LUMO energy level of a material is higher than the HOMO energy level of the same material. A “higher” HOMO or LUMO energy level appears closer to the top of such a diagram than a “lower” HOMO or LUMO energy level.

More details on OLEDs, and the definitions described above, can be found in U.S. Pat. No. 7,279,704, which is incorporated herein by reference in its entirety.

SUMMARY

A compound of the formula ML_(A)L_(B) where ligand L_(A) is of Formula I, and ligand L_(B) is of Formula II below.

wherein

M is selected from Os(II) or Ru(II), and the compound ML_(A)L_(B) has a formal neutral charge;

rings A, B, C, D, E, and F are independently a 5-membered or 6-membered aromatic ring, and R^(A), R^(B), R^(C), R^(D), R^(E), and R^(F) each independently represent mono to the maximum allowable substitution, or no substitution;

L¹, L², L³, and L⁴ independently represent a single bond or an organic linking group;

W¹, W², W³, and W⁴ are independently selected from carbon or nitrogen;

Y¹, Y², Y³, and Y⁴ are independently selected from carbon or nitrogen;

Z¹, Z², and Z³ are independently selected from carbon or nitrogen, and at least one of Z¹, Z², and Z³ is nitrogen;

wherein each R^(A), R^(B), R^(C), R^(D), R^(E), and R^(F) are independently hydrogen or a substituent selected from the group consisting of deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof, or optionally, any two adjacent substituents of R^(A), R^(B), R^(C), R^(D), R^(E), or R^(F), can join to form a ring.

An organic electroluminescent device that includes an anode, a cathode, and an organic layer comprising a compound of the formula ML_(A)L_(B) where ligand L_(A) is of Formula I, and ligand L_(B) is of Formula II above.

A consumer product comprising an organic light-emitting device (OLED), the OLED including an anode, a cathode, and an organic layer comprising a compound of the formula ML_(A)L_(B) where ligand L_(A) is of Formula I, and ligand L_(B) is of Formula II above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an organic light emitting device.

FIG. 2 shows an inverted organic light emitting device that does not have a separate electron transport layer.

DETAILED DESCRIPTION

Our prior work with bis-tridentate metal compounds and their application as phosphorescent emitters in OLEDs is described in WO 2009/046266, assigned to Universal Display Corporation, hereafter, the '266 Publication. One interest at that time was to develop phosphorescent emitters that emit in the blue region of the visible spectrum. The general structure of the tridentate ligand is shown below where ring A represents an aromatic ring system with two to four fused rings, ring B represents a 5- or 6-membered aromatic ring or an aromatic ring system as in ring A, and M is a second or third row transition metal.

Compounds of particular interest were neutral homoleptic compounds of Ru(II) or Os(II) with both ring A and ring B as cyclic N—N carbenes bridged by a central benzene ring. For example, some examples of ring A and ring B cyclic carbenes, and a particular Os(II) compound are shown below. The calculated triplet T1 energy values for es-1 was 496 nm, and therefore emit in a deep green region of the visible spectrum. Our present interest is to a similar class of bis-tridentate Os(II) or Ru(II) compounds, which emit in the yellow to orange to red and even into the infra-red region of the spectrum, e.g., from about 560 nm to about 1200 nm, which is a very significant operation design range, particularly into the near-IR. To achieve this objective we investigated a class of heteroleptic bis-tridentate Os(II) and Ru(II) complexes, and to our surprise we observed not just a small shift, but rather a significant red shift in the emission from the prior homoleptic Os(II) carbene compounds of the '266 Publication.

Generally, an OLED comprises at least one organic layer disposed between and electrically connected to an anode and a cathode. When a current is applied, the anode injects holes and the cathode injects electrons into the organic layer(s). The injected holes and electrons each migrate toward the oppositely charged electrode. When an electron and hole localize on the same molecule, an “exciton,” which is a localized electron-hole pair having an excited energy state, is formed. Light is emitted when the exciton relaxes via a photoemissive mechanism. In some cases, the exciton may be localized on an excimer or an exciplex. Non-radiative mechanisms, such as thermal relaxation, may also occur, but are generally considered undesirable.

The initial OLEDs used emissive molecules that emitted light from their singlet states (“fluorescence”) as disclosed, for example, in U.S. Pat. No. 4,769,292, which is incorporated by reference in its entirety. Fluorescent emission generally occurs in a time frame of less than 10 nanoseconds.

More recently, OLEDs having emissive materials that emit light from triplet states (“phosphorescence”) have been demonstrated. Baldo et al., “Highly Efficient Phosphorescent Emission from Organic Electroluminescent Devices,” Nature, vol. 395, 151-154, 1998; (“Baldo-I”) and Baldo et al., “Very high-efficiency green organic light-emitting devices based on electrophosphorescence,” Appl. Phys. Lett., vol. 75, No. 3, 4-6 (1999) (“Baldo-II”), are incorporated by reference in their entireties. Phosphorescence is described in more detail in U.S. Pat. No. 7,279,704 at cols. 5-6, which are incorporated by reference.

FIG. 1 shows an organic light emitting device 100. The figures are not necessarily drawn to scale. Device 100 may include a substrate 110, an anode 115, a hole injection layer 120, a hole transport layer 125, an electron blocking layer 130, an emissive layer 135, a hole blocking layer 140, an electron transport layer 145, an electron injection layer 150, a protective layer 155, a cathode 160, and a barrier layer 170. Cathode 160 is a compound cathode having a first conductive layer 162 and a second conductive layer 164. Device 100 may be fabricated by depositing the layers described, in order. The properties and functions of these various layers, as well as example materials, are described in more detail in U.S. Pat. No. 7,279,704 at cols. 6-10, which are incorporated by reference.

More examples for each of these layers are available. For example, a flexible and transparent substrate-anode combination is disclosed in U.S. Pat. No. 5,844,363, which is incorporated by reference in its entirety. An example of a p-doped hole transport layer is m-MTDATA doped with F₄-TCNQ at a molar ratio of 50:1, as disclosed in U.S. Patent Application Publication No. 2003/0230980, which is incorporated by reference in its entirety. Examples of emissive and host materials are disclosed in U.S. Pat. No. 6,303,238 to Thompson et al., which is incorporated by reference in its entirety. An example of an n-doped electron transport layer is BPhen doped with Li at a molar ratio of 1:1, as disclosed in U.S. Patent Application Publication No. 2003/0230980, which is incorporated by reference in its entirety. U.S. Pat. Nos. 5,703,436 and 5,707,745, which are incorporated by reference in their entireties, disclose examples of cathodes including compound cathodes having a thin layer of metal such as Mg:Ag with an overlying transparent, electrically-conductive, sputter-deposited ITO layer. The theory and use of blocking layers is described in more detail in U.S. Pat. No. 6,097,147 and U.S. Patent Application Publication No. 2003/0230980, which are incorporated by reference in their entireties. Examples of injection layers are provided in U.S. Patent Application Publication No. 2004/0174116, which is incorporated by reference in its entirety. A description of protective layers may be found in U.S. Patent Application Publication No. 2004/0174116, which is incorporated by reference in its entirety.

FIG. 2 shows an inverted OLED 200. The device includes a substrate 210, a cathode 215, an emissive layer 220, a hole transport layer 225, and an anode 230. Device 200 may be fabricated by depositing the layers described, in order. Because the most common OLED configuration has a cathode disposed over the anode, and device 200 has cathode 215 disposed under anode 230, device 200 may be referred to as an “inverted” OLED. Materials similar to those described with respect to device 100 may be used in the corresponding layers of device 200. FIG. 2 provides one example of how some layers may be omitted from the structure of device 100.

The simple layered structure illustrated in FIGS. 1 and 2 is provided by way of non-limiting example, and it is understood that embodiments of the invention may be used in connection with a wide variety of other structures. The specific materials and structures described are exemplary in nature, and other materials and structures may be used. Functional OLEDs may be achieved by combining the various layers described in different ways, or layers may be omitted entirely, based on design, performance, and cost factors. Other layers not specifically described may also be included. Materials other than those specifically described may be used. Although many of the examples provided herein describe various layers as comprising a single material, it is understood that combinations of materials, such as a mixture of host and dopant, or more generally a mixture, may be used. Also, the layers may have various sublayers. The names given to the various layers herein are not intended to be strictly limiting. For example, in device 200, hole transport layer 225 transports holes and injects holes into emissive layer 220, and may be described as a hole transport layer or a hole injection layer. In one embodiment, an OLED may be described as having an “organic layer” disposed between a cathode and an anode. This organic layer may comprise a single layer, or may further comprise multiple layers of different organic materials as described, for example, with respect to FIGS. 1 and 2.

Structures and materials not specifically described may also be used, such as OLEDs comprised of polymeric materials (PLEDs) such as disclosed in U.S. Pat. No. 5,247,190 to Friend et al., which is incorporated by reference in its entirety. By way of further example, OLEDs having a single organic layer may be used. OLEDs may be stacked, for example as described in U.S. Pat. No. 5,707,745 to Forrest et al, which is incorporated by reference in its entirety. The OLED structure may deviate from the simple layered structure illustrated in FIGS. 1 and 2. For example, the substrate may include an angled reflective surface to improve out-coupling, such as a mesa structure as described in U.S. Pat. No. 6,091,195 to Forrest et al., and/or a pit structure as described in U.S. Pat. No. 5,834,893 to Bulovic et al., which are incorporated by reference in their entireties.

Unless otherwise specified, any of the layers of the various embodiments may be deposited by any suitable method. For the organic layers, preferred methods include thermal evaporation, ink-jet, such as described in U.S. Pat. Nos. 6,013,982 and 6,087,196, which are incorporated by reference in their entireties, organic vapor phase deposition (OVPD), such as described in U.S. Pat. No. 6,337,102 to Forrest et al., which is incorporated by reference in its entirety, and deposition by organic vapor jet printing (OVJP), such as described in U.S. Pat. No. 7,431,968, which is incorporated by reference in its entirety. Other suitable deposition methods include spin coating and other solution based processes. Solution based processes are preferably carried out in nitrogen or an inert atmosphere. For the other layers, preferred methods include thermal evaporation. Preferred patterning methods include deposition through a mask, cold welding such as described in U.S. Pat. Nos. 6,294,398 and 6,468,819, which are incorporated by reference in their entireties, and patterning associated with some of the deposition methods such as ink-jet and organic vapor jet printing (OVJP). Other methods may also be used. The materials to be deposited may be modified to make them compatible with a particular deposition method. For example, substituents such as alkyl and aryl groups, branched or unbranched, and preferably containing at least 3 carbons, may be used in small molecules to enhance their ability to undergo solution processing. Substituents having 20 carbons or more may be used, and 3-20 carbons is a preferred range. Materials with asymmetric structures may have better solution processability than those having symmetric structures, because asymmetric materials may have a lower tendency to recrystallize. Dendrimer substituents may be used to enhance the ability of small molecules to undergo solution processing.

Devices fabricated in accordance with embodiments of the present invention may further optionally comprise a barrier layer. One purpose of the barrier layer is to protect the electrodes and organic layers from damaging exposure to harmful species in the environment including moisture, vapor and/or gases, etc. The barrier layer may be deposited over, under or next to a substrate, an electrode, or over any other parts of a device including an edge. The barrier layer may comprise a single layer, or multiple layers. The barrier layer may be formed by various known chemical vapor deposition techniques and may include compositions having a single phase as well as compositions having multiple phases. Any suitable material or combination of materials may be used for the barrier layer. The barrier layer may incorporate an inorganic or an organic compound or both. The preferred barrier layer comprises a mixture of a polymeric material and a non-polymeric material as described in U.S. Pat. No. 7,968,146, PCT Pat. Application Nos. PCT/US2007/023098 and PCT/US2009/042829, which are herein incorporated by reference in their entireties. To be considered a “mixture”, the aforesaid polymeric and non-polymeric materials comprising the barrier layer should be deposited under the same reaction conditions and/or at the same time. The weight ratio of polymeric to non-polymeric material may be in the range of 95:5 to 5:95. The polymeric material and the non-polymeric material may be created from the same precursor material. In one example, the mixture of a polymeric material and a non-polymeric material consists essentially of polymeric silicon and inorganic silicon.

Devices fabricated in accordance with embodiments of the invention can be incorporated into a wide variety of electronic component modules (or units) that can be incorporated into a variety of electronic products or intermediate components. Examples of such electronic products or intermediate components include display screens, lighting devices such as discrete light source devices or lighting panels, etc. that can be utilized by the end-user product manufacturers. Such electronic component modules can optionally include the driving electronics and/or power source(s). Devices fabricated in accordance with embodiments of the invention can be incorporated into a wide variety of consumer products that have one or more of the electronic component modules (or units) incorporated therein. A consumer product comprising an OLED that includes the compound of the present disclosure in the organic layer in the OLED is disclosed. Such consumer products would include any kind of products that include one or more light source(s) and/or one or more of some type of visual displays. Some examples of such consumer products include flat panel displays, curved displays, computer monitors, medical monitors, televisions, billboards, lights for interior or exterior illumination and/or signaling, heads-up displays, fully or partially transparent displays, flexible displays, rollable displays, foldable displays, stretchable displays, laser printers, telephones, mobile phones, tablets, phablets, personal digital assistants (PDAs), wearable devices, laptop computers, digital cameras, camcorders, viewfinders, micro-displays (displays that are less than 2 inches diagonal), 3-D displays, virtual reality or augmented reality displays, vehicles, video walls comprising multiple displays tiled together, theater or stadium screen, a light therapy device, and a sign. Various control mechanisms may be used to control devices fabricated in accordance with the present invention, including passive matrix and active matrix. Many of the devices are intended for use in a temperature range comfortable to humans, such as 18 degrees C. to 30 degrees C., and more preferably at room temperature (20-25 degrees C.), but could be used outside this temperature range, for example, from −40 degree C. to +80 degree C.

The materials and structures described herein may have applications in devices other than OLEDs. For example, other optoelectronic devices such as organic solar cells and organic photodetectors may employ the materials and structures. More generally, organic devices, such as organic transistors, may employ the materials and structures.

The terms “halo,” “halogen,” and “halide” are used interchangeably and refer to fluorine, chlorine, bromine, and iodine.

The term “acyl” refers to a substituted carbonyl radical (C(O)—R_(s)).

The term “ester” refers to a substituted oxycarbonyl (—O—C(O)—R_(s) or —C(O)—O—R_(s)) radical.

The term “ether” refers to an —OR_(s) radical.

The terms “sulfanyl” or “thio-ether” are used interchangeably and refer to a —SR_(s) radical.

The term “sulfinyl” refers to a —S(O)—R_(s) radical.

The term “sulfonyl” refers to a —SO₂—R_(s) radical.

The term “phosphino” refers to a —P(R_(s))₃ radical, wherein each R_(s) can be same or different.

The term “silyl” refers to a —Si(R_(s))₃ radical, wherein each R_(s) can be same or different.

In each of the above, R_(s) can be hydrogen or a substituent selected from the group consisting of deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, and combination thereof. Preferred R_(s) is selected from the group consisting of alkyl, cycloalkyl, aryl, heteroaryl, and combination thereof.

The term “alkyl” refers to and includes both straight and branched chain alkyl radicals. Preferred alkyl groups are those containing from one to fifteen carbon atoms and includes methyl, ethyl, propyl, 1-methylethyl, butyl, 1-methylpropyl, 2-methylpropyl, pentyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 1,1-dimethylpropyl, 1,2-dimethylpropyl, 2,2-dimethylpropyl, and the like. Additionally, the alkyl group is optionally substituted.

The term “cycloalkyl” refers to and includes monocyclic, polycyclic, and spiro alkyl radicals. Preferred cycloalkyl groups are those containing 3 to 12 ring carbon atoms and includes cyclopropyl, cyclopentyl, cyclohexyl, bicyclo[3.1.1]heptyl, spiro[4.5]decyl, spiro[5.5]undecyl, adamantyl, and the like. Additionally, the cycloalkyl group is optionally substituted.

The terms “heteroalkyl” or “heterocycloalkyl” refer to an alkyl or a cycloalkyl radical, respectively, having at least one carbon atom replaced by a heteroatom. Optionally the at least one heteroatom is selected from O, S, N, P, B, Si and Se, preferably, O, S or N. Additionally, the heteroalkyl or heterocycloalkyl group is optionally substituted.

The term “alkenyl” refers to and includes both straight and branched chain alkene radicals. Alkenyl groups are essentially alkyl groups that include at least one carbon-carbon double bond in the alkyl chain. Cycloalkenyl groups are essentially cycloalkyl groups that include at least one carbon-carbon double bond in the cycloalkyl ring. The term “heteroalkenyl” as used herein refers to an alkenyl radical having at least one carbon atom replaced by a heteroatom. Optionally the at least one heteroatom is selected from O, S, N, P, B, Si, and Se, preferably, O, S, or N. Preferred alkenyl, cycloalkenyl, or heteroalkenyl groups are those containing two to fifteen carbon atoms. Additionally, the alkenyl, cycloalkenyl, or heteroalkenyl group is optionally substituted.

The term “alkynyl” refers to and includes both straight and branched chain alkyne radicals. Preferred alkynyl groups are those containing two to fifteen carbon atoms. Additionally, the alkynyl group is optionally substituted.

The terms “aralkyl” or “arylalkyl” are used interchangeably and refer to an alkyl group that is substituted with an aryl group. Additionally, the aralkyl group is optionally substituted.

The term “heterocyclic group” refers to and includes aromatic and non-aromatic cyclic radicals containing at least one heteroatom. Optionally the at least one heteroatom is selected from O, S, N, P, B, Si, and Se, preferably, O, S, or N. Hetero-aromatic cyclic radicals may be used interchangeably with heteroaryl. Preferred hetero-non-aromatic cyclic groups are those containing 3 to 7 ring atoms which includes at least one hetero atom, and includes cyclic amines such as morpholino, piperidino, pyrrolidino, and the like, and cyclic ethers/thio-ethers, such as tetrahydrofuran, tetrahydropyran, tetrahydrothiophene, and the like. Additionally, the heterocyclic group may be optionally substituted.

The term “aryl” refers to and includes both single-ring aromatic hydrocarbyl groups and polycyclic aromatic ring systems. The polycyclic rings may have two or more rings in which two carbons are common to two adjoining rings (the rings are “fused”) wherein at least one of the rings is an aromatic hydrocarbyl group, e.g., the other rings can be cycloalkyls, cycloalkenyls, aryl, heterocycles, and/or heteroaryls. Preferred aryl groups are those containing six to thirty carbon atoms, preferably six to twenty carbon atoms, more preferably six to twelve carbon atoms. Especially preferred is an aryl group having six carbons, ten carbons or twelve carbons. Suitable aryl groups include phenyl, biphenyl, triphenyl, triphenylene, tetraphenylene, naphthalene, anthracene, phenalene, phenanthrene, fluorene, pyrene, chrysene, perylene, and azulene, preferably phenyl, biphenyl, triphenyl, triphenylene, fluorene, and naphthalene. Additionally, the aryl group is optionally substituted.

The term “heteroaryl” refers to and includes both single-ring aromatic groups and polycyclic aromatic ring systems that include at least one heteroatom. The heteroatoms include, but are not limited to O, S, N, P, B, Si, and Se. In many instances, O, S, or N are the preferred heteroatoms. Hetero-single ring aromatic systems are preferably single rings with 5 or 6 ring atoms, and the ring can have from one to six heteroatoms. The hetero-polycyclic ring systems can have two or more rings in which two atoms are common to two adjoining rings (the rings are “fused”) wherein at least one of the rings is a heteroaryl, e.g., the other rings can be cycloalkyls, cycloalkenyls, aryl, heterocycles, and/or heteroaryls. The hetero-polycyclic aromatic ring systems can have from one to six heteroatoms per ring of the polycyclic aromatic ring system. Preferred heteroaryl groups are those containing three to thirty carbon atoms, preferably three to twenty carbon atoms, more preferably three to twelve carbon atoms. Suitable heteroaryl groups include dibenzothiophene, dibenzofuran, dibenzoselenophene, furan, thiophene, benzofuran, benzothiophene, benzoselenophene, carbazole, indolocarbazole, pyridylindole, pyrrolodipyridine, pyrazole, imidazole, triazole, oxazole, thiazole, oxadiazole, oxatriazole, dioxazole, thiadiazole, pyridine, pyridazine, pyrimidine, pyrazine, triazine, oxazine, oxathiazine, oxadiazine, indole, benzimidazole, indazole, indoxazine, benzoxazole, benzisoxazole, benzothiazole, quinoline, isoquinoline, cinnoline, quinazoline, quinoxaline, naphthyridine, phthalazine, pteridine, xanthene, acridine, phenazine, phenothiazine, phenoxazine, benzofuropyridine, furodipyridine, benzothienopyridine, thienodipyridine, benzoselenophenopyridine, and selenophenodipyridine, preferably dibenzothiophene, dibenzofuran, dibenzoselenophene, carbazole, indolocarbazole, imidazole, pyridine, triazine, benzimidazole, 1,2-azaborine, 1,3-azaborine, 1,4-azaborine, borazine, and aza-analogs thereof. Additionally, the heteroaryl group is optionally substituted.

Of the aryl and heteroaryl groups listed above, the groups of triphenylene, naphthalene, anthracene, dibenzothiophene, dibenzofuran, dibenzoselenophene, carbazole, indolocarbazole, imidazole, pyridine, pyrazine, pyrimidine, triazine, and benzimidazole, and the respective aza-analogs of each thereof are of particular interest.

The terms alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aralkyl, heterocyclic group, aryl, and heteroaryl, as used herein, are independently unsubstituted, or independently substituted, with one or more general substituents.

In many instances, the general substituents are selected from the group consisting of deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.

In some instances, the preferred general substituents are selected from the group consisting of deuterium, fluorine, alkyl, cycloalkyl, heteroalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, aryl, heteroaryl, nitrile, isonitrile, sulfanyl, and combinations thereof.

In some instances, the preferred general substituents are selected from the group consisting of deuterium, fluorine, alkyl, cycloalkyl, alkoxy, aryloxy, amino, silyl, aryl, heteroaryl, sulfanyl, and combinations thereof.

In yet other instances, the more preferred general substituents are selected from the group consisting of deuterium, fluorine, alkyl, cycloalkyl, aryl, heteroaryl, and combinations thereof.

The terms “substituted” and “substitution” refer to a substituent other than H that is bonded to the relevant position, e.g., a carbon or nitrogen. For example, when R¹ represents mono-substitution, then one R¹ must be other than H (i.e., a substitution). Similarly, when R¹ represents di-substitution, then two of R¹ must be other than H. Similarly, when R¹ represents no substitution, R¹, for example, can be a hydrogen for available valencies of ring atoms, as in carbon atoms for benzene and the nitrogen atom in pyrrole, or simply represents nothing for ring atoms with fully filled valencies, e.g., the nitrogen atom in pyridine. The maximum number of substitutions possible in a ring structure will depend on the total number of available valencies in the ring atoms.

As used herein, “combinations thereof” indicates that one or more members of the applicable list are combined to form a known or chemically stable arrangement that one of ordinary skill in the art can envision from the applicable list. For example, an alkyl and deuterium can be combined to form a partial or fully deuterated alkyl group; a halogen and alkyl can be combined to form a halogenated alkyl substituent; and a halogen, alkyl, and aryl can be combined to form a halogenated arylalkyl. In one instance, the term substitution includes a combination of two to four of the listed groups. In another instance, the term substitution includes a combination of two to three groups. In yet another instance, the term substitution includes a combination of two groups. Preferred combinations of substituent groups are those that contain up to fifty atoms that are not hydrogen or deuterium, or those which include up to forty atoms that are not hydrogen or deuterium, or those that include up to thirty atoms that are not hydrogen or deuterium. In many instances, a preferred combination of substituent groups will include up to twenty atoms that are not hydrogen or deuterium.

The “aza” designation in the fragments described herein, i.e. aza-dibenzofuran, aza-dibenzothiophene, etc. means that one or more of the C—H groups in the respective fragment can be replaced by a nitrogen atom, for example, and without any limitation, azatriphenylene encompasses both dibenzo[f,h]quinoxaline and dibenzo[f,h]quinoline. One of ordinary skill in the art can readily envision other nitrogen analogs of the aza-derivatives described above, and all such analogs are intended to be encompassed by the terms as set forth herein.

As used herein, “deuterium” refers to an isotope of hydrogen. Deuterated compounds can be readily prepared using methods known in the art. For example, U.S. Pat. No. 8,557,400, Patent Pub. No. WO 2006/095951, and U.S. Pat. Application Pub. No. US 2011/0037057, which are hereby incorporated by reference in their entireties, describe the making of deuterium-substituted organometallic complexes. Further reference is made to Ming Yan, et al., Tetrahedron 2015, 71, 1425-30 and Atzrodt et al., Angew. Chem. Int. Ed. (Reviews) 2007, 46, 7744-65, which are incorporated by reference in their entireties, describe the deuteration of the methylene hydrogens in benzyl amines and efficient pathways to replace aromatic ring hydrogens with deuterium, respectively.

It is to be understood that when a molecular fragment is described as being a substituent or otherwise attached to another moiety, its name may be written as if it were a fragment (e.g. phenyl, phenylene, naphthyl, dibenzofuryl) or as if it were the whole molecule (e.g. benzene, naphthalene, dibenzofuran). As used herein, these different ways of designating a substituent or attached fragment are considered to be equivalent.

The invention is directed to a compound of the formula ML_(A)L_(B) where ligand L_(A) is of Formula I and ligand L_(B) is of Formula II below.

wherein

M is selected from Os(II) or Ru(II), and the compound ML_(A)L_(B) has a formal neutral charge;

rings A, B, C, D, E, and F are independently a 5-membered or 6-membered aromatic ring, and R^(A), R^(B), R^(C), R^(D), R^(E), and R^(F) each independently represent mono to the maximum allowable substitution, or no substitution;

L¹, L², L³, and L⁴ independently represent a single bond or an organic linking group;

W¹, W², W³, and W⁴ are independently selected from carbon or nitrogen;

Y¹, Y², Y³, and Y⁴ are independently selected from carbon or nitrogen;

Z¹, Z², and Z³ are independently selected from carbon or nitrogen, and at least one of Z¹, Z², and Z³ is nitrogen;

wherein each R^(A), R^(B), R^(C), R^(D), R^(E), and R^(F) are independently hydrogen or a substituent selected from the group consisting of deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof, or optionally, any two adjacent substituents of R^(A), R^(B), R^(C), R^(D), R^(E), or R^(F), can join to form a ring.

In one embodiment, R^(A), R^(B), R^(C), R^(D), R^(E), and R^(F) are selected from hydrogen or a substituent selected from the group consisting of deuterium, fluorine, alkyl, cycloalkyl, heteroalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, aryl, heteroaryl, nitrile, isonitrile, sulfanyl, and combinations thereof.

In one embodiment of the compounds ML_(A)L_(B), ligand L_(B) is further defined by one of Z¹, Z², or Z³ as being nitrogen. In many instances, the one Z¹, Z², or Z³ nitrogen will form dative coordinate bonds with Os(II) or Ru(II), and the third of Z¹, Z², or Z³ will be a carbon. For example, ring E can be an optionally substituted benzene, naphthyl, or an aza-analog of each thereof, with Z² as carbon, and rings D and F are pyridyl or imidazole (Z¹ and Z³ are nitrogen). In another instance, one of Z¹ or Z³ is nitrogen, and the other is a carbene carbon.

In one embodiment of the compounds ML_(A)L_(B), ligand L_(B) is further defined by two of Z¹, Z², or Z³ as being nitrogen. In many instances, the two Z¹, Z², or Z³ nitrogen will form dative coordinate bonds with Os(II) or Ru(II), and the third of Z¹, Z², or Z³ will be a carbon. For example, ring E can be an optionally substituted benzene, naphthyl, or an aza-analog of each thereof, with Z² as carbon, and rings D and F are pyridyl or imidazole (Z¹ and Z³ are nitrogen). In another instance, one of Z¹ or Z³ is nitrogen, and the other is a carbene carbon.

In one embodiment of the compounds ML_(A)L_(B), ligand L_(B) is further defined by Z¹ as carbon, and ring D selected from an optionally substituted benzene, naphthyl, or an aza-analog of each thereof. Moreover, Z² and Z³ are nitrogen, or in another instance, one of Z² or Z³ is nitrogen, and the other is a carbene carbon.

In one embodiment of the compounds ML_(A)L_(B), ligand L_(B) is further defined by Z³ as carbon, and ring F selected from an optionally substituted benzene, naphthyl, or an aza-analog of each thereof. Moreover, Z¹ and Z² are nitrogen, or in another instance, one of Z¹ or Z² is nitrogen, and the other is a carbene carbon.

In one embodiment of the compounds ML_(A)L_(B), and optionally, in combination with the ligand L_(B) embodiments above, ligand L_(A) will have two of rings A, B, or C being an N-heterocyclic carbene ring, each of which with a carbene carbon coordinated to Os(II) or Ru(II).

In another embodiment of the compounds ML_(A)L_(B), and optionally, in combination with the ligand L_(B) embodiments above, ring A and ring C are both N-heterocyclic carbene rings, each of which with a carbene carbon coordinated to Os(II) or Ru(II). Also, ring B can be selected from optionally substituted benzene, naphthyl, or an aza-analog of each thereof.

In another embodiment of the compounds ML_(A)L_(B), or in any one preferred embodiment of ligand L_(A) or ligand L_(B) above, L¹, L², L³, and L⁴ are each a direct bond.

In one embodiment of the compounds ML_(A)L_(B), or in any one preferred embodiment of ligand L_(A) or ligand L_(B) above, or where L¹, L², L³, and L⁴ are each a direct bond, each of W¹, W², W³, and W⁴ are carbon, and ring B is an optionally substituted benzene. In another embodiment, one or two of W¹, W², W³, or W⁴ are nitrogen, preferably, W¹ and/or W² are nitrogen, particularly if rings A and/or C are N-heterocyclic carbene ligand groups.

Of particular interest, are compounds ML_(A)L_(B), ligand L_(A) is selected from the group consisting of

wherein

X¹, X², X³, X⁴, and X⁵ are independently selected from C or N;

R, R′, R¹, R², and R³ are independently hydrogen or a substituent selected from the group consisting of deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acid, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; or optionally, any two adjacent substituents of R¹, R², and R³ can join to form a ring with ring.

In another embodiment, the above compounds of particular interest will have R^(A), R^(B), R^(C), R^(D), R^(E), and R^(F) as being selected from hydrogen or a substituent selected from the group consisting of deuterium, fluorine, alkyl, cycloalkyl, heteroalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, aryl, heteroaryl, nitrile, isonitrile, sulfanyl, and combinations thereof.

In another embodiment, the above compounds of particular interest will have each of X¹, X², and X³ is C, and form a benzene ring, which is optionally substituted with R².

In another embodiment, the above compounds of particular interest will have two of R¹, two of R², and/or two of R³ join to form a fused benzene ring or an aza-analog thereof. Again, each fused ring is optionally substituted. One reason for fusing an aromatic ring, preferably, a 6-membered aromatic ring to one or more of rings A, B, or C of ligand L_(A) is to provide additional red shift in the emission spectrum of the compounds ML_(A)L_(B), infra.

Select compounds of ML_(A)L_(B) will have a ligand L_(A) of Formula I selected from the group consisting of

Select compounds of ML_(A)L_(B) will have a ligand L_(B) of Formula II selected from the group consisting of

wherein

X⁶, X⁷, X⁸, X⁹, X¹⁰, X¹¹, X¹², X¹³, and X¹⁴ are each independently selected from C or N, and each 6-membered aromatic ring has no more than three N;

R″, R⁴, R⁵, and R⁶ are independently hydrogen or a substituent selected from the group consisting of deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; or optionally, any two adjacent substituents of R⁴, R⁵, and R⁶ can join to form a ring with ring.

Select embodiments of ligand L_(B) will have R⁴, R⁵, and R⁶ selected from hydrogen or a substituent selected from the group consisting of deuterium, fluorine, alkyl, cycloalkyl, heteroalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, aryl, heteroaryl, nitrile, isonitrile, sulfanyl, and combinations thereof.

In another embodiment, the compounds with the select embodiments of L_(B) will have each of X⁶, X⁷, and X⁸ as carbon, and form a benzene or pyridine ring, which is optionally substituted with R⁴. In another embodiment, the compounds with the select embodiments of L_(B) will have each of X⁹, X¹⁰, and X¹¹ as carbon, and form a benzene or pyridine ring, which is optionally substituted with R⁵. In another embodiment, the compounds with the select embodiments of L_(B) will have each of X¹², X¹³, and X¹⁴ as carbon, and form a benzene or pyridine ring, which is optionally substituted with R⁶.

In another embodiment, the above compounds with the select embodiments of L_(B) will have two of R⁴, two of R⁵, and/or two of R⁶ join to form a fused benzene ring or an aza-analog thereof. Again, each fused ring is optionally substituted. One reason for fusing an aromatic ring, preferably, a 6-membered aromatic ring to one or more of rings D, E, or F of ligand L_(B) is to provide additional red shift in the emission spectrum of the compounds ML_(A)L_(B), infra.

Compounds of particular interest will include any one of the select ligands LB above in combination with any one ligand LA selected from the group consisting of L_(A1) to L_(A68) identified above.

Select compounds of ML_(A)L_(B) will have a ligand L_(B) of Formula II selected from the group consisting of

We also describe a very select structural list of the compounds ML_(A)L_(B). These compounds can be assigned or identified as a Compound x having the formula M(L_(Ai))(L_(Bj)); wherein x=151i+j−151; a is an integer from 1 to 68; and j is an integer from 1 to 151. Ligand L_(Ai) will have a structure selected from ligand L_(A1) to LA₆₈, and Ligand L_(Bj) will have a structure selected from ligand L_(B1) to LA_(B151).

We also describe an organic light emitting device (OLED) comprising an anode, a cathode, and an organic layer disposed between the anode and the cathode, the organic layer comprising a compound of the formula ML_(A)L_(B); wherein ligand L_(A) is of Formula I, and ligand L_(B) is of Formula II

wherein

M is selected from Os(II) or Ru(II), and the compound ML_(A)L_(B) has a formal neutral charge;

rings A, B, C, D, E, and F are independently a 5-membered or 6-membered aromatic ring, and R^(A), R^(B), R^(C), R^(D), R^(E), and R^(F) each independently represent mono to the maximum allowable substitution, or no substitution;

L¹, L², L³, and L⁴ independently represent a single bond or an organic linking group;

W¹, W², W³, and W⁴ are independently selected from carbon or nitrogen;

Y¹, Y², Y³, and Y⁴ are independently selected from carbon or nitrogen;

Z¹, Z², and Z³ are independently selected from carbon or nitrogen, and at least one of Z¹, Z², and Z³ is nitrogen;

wherein each R^(A), R^(B), R^(C), R^(D), R^(E), and R^(F) are independently hydrogen or a substituent selected from the group consisting of deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof, or optionally, any two adjacent substituents of R^(A), R^(B), R^(C), R^(D), R^(E), or R^(F), can join to form a ring.

The compounds of ML_(A)L_(B) where ligand L_(A) is of Formula I and ligand L_(B) is of Formula II provides an extraordinary opportunity to color tune the emission of an OLED from green (compound 5 and 6), yellow (compound 3 and 4), red (compound 2) and even into the near-IR range (compound 7, 8 and 9). As indicated by the DFT data of Table 1 (see, experimental) the heteroleptic, bis tridenate Os(II)-carbene compounds, e.g. compounds 2-9, provide an operating design range to extend the light emission of a phosphorescent OLED from about 550 nm to about 1200 nm by simply changing out the bis-carbene ligand of Comparative Example 1 (CE1) for a tridentate L_(B) ligand with a coordinating quinazoline (Compound 2) at one of the six octahedral sites—there is no other change in the octahedral environment about the Os(II). The red shift in this instance is a huge red-shift of about 275 nm from CE1 to Compound 2. Similar comparisons can be made between CE1 and any one of Compounds 3 to 9. For example, the switching out of another octahedral site with another quinazoline as in Compound 9 provides a red shift of about 677 nm.

Of particular interest are compounds ML_(A)L_(B) where ligand L_(A) is of Formula I and ligand L_(B) is of Formula II that emit in the near-IR region of the spectrum, i.e., from 700 nm to 1200 nm, from 800 nm to 1200 nm, from 900 nm to 1200 nm, and from 1000 nm to 1200 nm.

In some embodiments, the OLED has one or more characteristics selected from the group consisting of being flexible, being rollable, being foldable, being stretchable, and being curved. In some embodiments, the OLED is transparent or semi-transparent. In some embodiments, the OLED further comprises a layer comprising carbon nanotubes.

In some embodiments, the OLED further comprises a layer comprising a delayed fluorescent emitter. In some embodiments, the OLED comprises a RGB pixel arrangement or white plus color filter pixel arrangement. In some embodiments, the OLED is a mobile device, a hand held device, or a wearable device. In some embodiments, the OLED is a display panel having less than 10 inch diagonal or 50 square inch area. In some embodiments, the OLED is a display panel having at least 10 inch diagonal or 50 square inch area. In some embodiments, the OLED is a lighting panel.

According to another aspect, an emissive region in an OLED (e.g., the organic layer described herein) is disclosed. The emissive region comprises a first compound as described herein. In some embodiments, the first compound in the emissive region is an emissive dopant or a non-emissive dopant. In some embodiments, the emissive dopant further comprises a host, wherein the host comprises at least one selected from the group consisting of metal complex, triphenylene, carbazole, dibenzothiophene, dibenzofuran, dibenzoselenophene, aza-triphenylene, aza-carbazole, aza-dibenzothiophene, aza-dibenzofuran, and aza-dibenzoselenophene. In some embodiments, the emissive region further comprises a host, wherein the host is selected from the group consisting of:

and combinations thereof.

The organic layer can also include a host. In some embodiments, two or more hosts are preferred. In some embodiments, the hosts used may be a) bipolar, b) electron transporting, c) hole transporting or d) wide band gap materials that play little role in charge transport. In some embodiments, the host can include a metal complex. The host can be a triphenylene containing benzo-fused thiophene or benzo-fused furan. Any substituent in the host can be an unfused substituent independently selected from the group consisting of C_(n)H_(2n+1), OC_(n)H_(2n+1), OAr₁, N(C_(n)H_(2n+1))₂, N(Ar₁)(Ar₂), CH═CH—C_(n)H_(2n+1), C≡C—C_(n)H_(2n+1), Ar₁, Ar₁—Ar₂, and C_(n)H_(2n)—Ar₁, or the host has no substitutions. In the preceding substituents n can range from 1 to 10; and Ar₁ and Ar₂ can be independently selected from the group consisting of benzene, biphenyl, naphthalene, triphenylene, carbazole, and heteroaromatic analogs thereof. The host can be an inorganic compound. For example a Zn containing inorganic material e.g. ZnS.

In some embodiments, the compound can be an emissive dopant. In some embodiments, the compound can produce emissions via phosphorescence, fluorescence, thermally activated delayed fluorescence, i.e., TADF (also referred to as E-type delayed fluorescence; see, e.g., U.S. application Ser. No. 15/700,352, which is hereby incorporated by reference in its entirety), triplet-triplet annihilation, or combinations of these processes. In some embodiments, the emissive dopant can be a racemic mixture, or can be enriched in one enantiomer.

According to another aspect, a formulation comprising the compound described herein is also disclosed.

The OLED disclosed herein can be incorporated into one or more of a consumer product, an electronic component module, and a lighting panel. The organic layer can be an emissive layer and the compound can be an emissive dopant in some embodiments, while the compound can be a non-emissive dopant in other embodiments.

In yet another aspect of the present disclosure, a formulation that comprises the novel compound disclosed herein is described. The formulation can include one or more components selected from the group consisting of a solvent, a host, a hole injection material, hole transport material, electron blocking material, hole blocking material, and an electron transport material, disclosed herein.

Combination with Other Materials

The materials described herein as useful for a particular layer in an organic light emitting device may be used in combination with a wide variety of other materials present in the device. For example, emissive dopants disclosed herein may be used in conjunction with a wide variety of hosts, transport layers, blocking layers, injection layers, electrodes and other layers that may be present. The materials described or referred to below are non-limiting examples of materials that may be useful in combination with the compounds disclosed herein, and one of skill in the art can readily consult the literature to identify other materials that may be useful in combination.

Conductivity Dopants:

A charge transport layer can be doped with conductivity dopants to substantially alter its density of charge carriers, which will in turn alter its conductivity. The conductivity is increased by generating charge carriers in the matrix material, and depending on the type of dopant, a change in the Fermi level of the semiconductor may also be achieved. Hole-transporting layer can be doped by p-type conductivity dopants and n-type conductivity dopants are used in the electron-transporting layer.

Non-limiting examples of the conductivity dopants that may be used in an OLED in combination with materials disclosed herein are exemplified below together with references that disclose those materials: EP01617493, EP01968131, EP2020694, EP2684932, US20050139810, US20070160905, US20090167167, US2010288362, WO06081780, WO2009003455, WO2009008277, WO2009011327, WO2014009310, US2007252140, US2015060804, US20150123047, and US2012146012.

HIL/HTL:

A hole injecting/transporting material to be used in the present invention is not particularly limited, and any compound may be used as long as the compound is typically used as a hole injecting/transporting material. Examples of the material include, but are not limited to: a phthalocyanine or porphyrin derivative; an aromatic amine derivative; an indolocarbazole derivative; a polymer containing fluorohydrocarbon; a polymer with conductivity dopants; a conducting polymer, such as PEDOT/PSS; a self-assembly monomer derived from compounds such as phosphonic acid and silane derivatives; a metal oxide derivative, such as MoO_(x); a p-type semiconducting organic compound, such as 1,4,5,8,9,12-Hexaazatriphenylenehexacarbonitrile; a metal complex, and a cross-linkable compounds.

Examples of aromatic amine derivatives used in HIL or HTL include, but not limit to the following general structures:

Each of Ar¹ to Ar⁹ is selected from the group consisting of aromatic hydrocarbon cyclic compounds such as benzene, biphenyl, triphenyl, triphenylene, naphthalene, anthracene, phenalene, phenanthrene, fluorene, pyrene, chrysene, perylene, and azulene; the group consisting of aromatic heterocyclic compounds such as dibenzothiophene, dibenzofuran, dibenzoselenophene, furan, thiophene, benzofuran, benzothiophene, benzoselenophene, carbazole, indolocarbazole, pyridylindole, pyrrolodipyridine, pyrazole, imidazole, triazole, oxazole, thiazole, oxadiazole, oxatriazole, dioxazole, thiadiazole, pyridine, pyridazine, pyrimidine, pyrazine, triazine, oxazine, oxathiazine, oxadiazine, indole, benzimidazole, indazole, indoxazine, benzoxazole, benzisoxazole, benzothiazole, quinoline, isoquinoline, cinnoline, quinazoline, quinoxaline, naphthyridine, phthalazine, pteridine, xanthene, acridine, phenazine, phenothiazine, phenoxazine, benzofuropyridine, furodipyridine, benzothienopyridine, thienodipyridine, benzoselenophenopyridine, and selenophenodipyridine; and the group consisting of 2 to 10 cyclic structural units which are groups of the same type or different types selected from the aromatic hydrocarbon cyclic group and the aromatic heterocyclic group and are bonded to each other directly or via at least one of oxygen atom, nitrogen atom, sulfur atom, silicon atom, phosphorus atom, boron atom, chain structural unit and the aliphatic cyclic group. Each Ar may be unsubstituted or may be substituted by a substituent selected from the group consisting of deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acids, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.

In one aspect, Ar¹ to Ar⁹ is independently selected from the group consisting of:

wherein k is an integer from 1 to 20; X¹⁰¹ to X¹⁰⁸ is C (including CH) or N; Z¹⁰¹ is NAr¹, O, or S; Ar¹ has the same group defined above.

Examples of metal complexes used in HIL or HTL include, but are not limited to the following general formula:

wherein Met is a metal, which can have an atomic weight greater than 40; (Y¹⁰¹-Y¹⁰²) is a bidentate ligand, Y¹⁰¹ and Y¹⁰² are independently selected from C, N, O, P, and S; L¹⁰¹ is an ancillary ligand; k′ is an integer value from 1 to the maximum number of ligands that may be attached to the metal; and k′+k″ is the maximum number of ligands that may be attached to the metal.

In one aspect, (Y¹⁰¹-Y¹⁰²) is a 2-phenylpyridine derivative. In another aspect, (Y¹⁰¹-Y¹⁰²) is a carbene ligand. In another aspect, Met is selected from Ir, Pt, Os, and Zn. In a further aspect, the metal complex has a smallest oxidation potential in solution vs. Fc⁺/Fc couple less than about 0.6 V.

Non-limiting examples of the HIL and HTL materials that may be used in an OLED in combination with materials disclosed herein are exemplified below together with references that disclose those materials: CN102702075, DE102012005215, EP01624500, EP01698613, EP01806334, EP01930964, EP01972613, EP01997799, EP02011790, EP02055700, EP02055701, EP1725079, EP2085382, EP2660300, EP650955, JP07-073529, JP2005112765, JP2007091719, JP2008021687, JP2014-009196, KR20110088898, KR20130077473, TW201139402, U.S. Ser. No. 06/517,957, US20020158242, US20030162053, US20050123751, US20060182993, US20060240279, US20070145888, US20070181874, US20070278938, US20080014464, US20080091025, US20080106190, US20080124572, US20080145707, US20080220265, US20080233434, US20080303417, US2008107919, US20090115320, US20090167161, US2009066235, US2011007385, US20110163302, US2011240968, US2011278551, US2012205642, US2013241401, US20140117329, US2014183517, U.S. Pat. Nos. 5,061,569, 5,639,914, WO05075451, WO07125714, WO08023550, WO08023759, WO2009145016, WO2010061824, WO2011075644, WO2012177006, WO2013018530, WO2013039073, WO2013087142, WO2013118812, WO2013120577, WO2013157367, WO2013175747, WO2014002873, WO2014015935, WO2014015937, WO2014030872, WO2014030921, WO2014034791, WO2014104514, WO2014157018.

EBL:

An electron blocking layer (EBL) may be used to reduce the number of electrons and/or excitons that leave the emissive layer. The presence of such a blocking layer in a device may result in substantially higher efficiencies, and/or longer lifetime, as compared to a similar device lacking a blocking layer. Also, a blocking layer may be used to confine emission to a desired region of an OLED. In some embodiments, the EBL material has a higher LUMO (closer to the vacuum level) and/or higher triplet energy than the emitter closest to the EBL interface. In some embodiments, the EBL material has a higher LUMO (closer to the vacuum level) and/or higher triplet energy than one or more of the hosts closest to the EBL interface. In one aspect, the compound used in EBL contains the same molecule or the same functional groups used as one of the hosts described below.

Host:

The light emitting layer of the organic EL device of the present invention preferably contains at least a metal complex as light emitting material, and may contain a host material using the metal complex as a dopant material. Examples of the host material are not particularly limited, and any metal complexes or organic compounds may be used as long as the triplet energy of the host is larger than that of the dopant. Any host material may be used with any dopant so long as the triplet criteria is satisfied.

Examples of metal complexes used as host are preferred to have the following general formula:

wherein Met is a metal; (Y¹⁰³-Y¹⁰⁴) is a bidentate ligand, Y¹⁰³ and Y¹⁰⁴ are independently selected from C, N, O, P, and S; L¹⁰¹ is an another ligand; k′ is an integer value from 1 to the maximum number of ligands that may be attached to the metal; and k′+k″ is the maximum number of ligands that may be attached to the metal.

In one aspect, the metal complexes are:

wherein (O—N) is a bidentate ligand, having metal coordinated to atoms O and N.

In another aspect, Met is selected from Ir and Pt. In a further aspect, (Y¹⁰³-Y¹⁰⁴) is a carbene ligand.

Examples of other organic compounds used as host are selected from the group consisting of aromatic hydrocarbon cyclic compounds such as benzene, biphenyl, triphenyl, triphenylene, tetraphenylene, naphthalene, anthracene, phenalene, phenanthrene, fluorene, pyrene, chrysene, perylene, and azulene; the group consisting of aromatic heterocyclic compounds such as dibenzothiophene, dibenzofuran, dibenzoselenophene, furan, thiophene, benzofuran, benzothiophene, benzoselenophene, carbazole, indolocarbazole, pyridylindole, pyrrolodipyridine, pyrazole, imidazole, triazole, oxazole, thiazole, oxadiazole, oxatriazole, dioxazole, thiadiazole, pyridine, pyridazine, pyrimidine, pyrazine, triazine, oxazine, oxathiazine, oxadiazine, indole, benzimidazole, indazole, indoxazine, benzoxazole, benzisoxazole, benzothiazole, quinoline, isoquinoline, cinnoline, quinazoline, quinoxaline, naphthyridine, phthalazine, pteridine, xanthene, acridine, phenazine, phenothiazine, phenoxazine, benzofuropyridine, furodipyridine, benzothienopyridine, thienodipyridine, benzoselenophenopyridine, and selenophenodipyridine; and the group consisting of 2 to 10 cyclic structural units which are groups of the same type or different types selected from the aromatic hydrocarbon cyclic group and the aromatic heterocyclic group and are bonded to each other directly or via at least one of oxygen atom, nitrogen atom, sulfur atom, silicon atom, phosphorus atom, boron atom, chain structural unit and the aliphatic cyclic group. Each option within each group may be unsubstituted or may be substituted by a substituent selected from the group consisting of deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acids, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.

In one aspect, the host compound contains at least one of the following groups in the molecule:

wherein R¹⁰¹ is selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acids, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof, and when it is aryl or heteroaryl, it has the similar definition as Ar's mentioned above. k is an integer from 0 to 20 or 1 to 20. X¹⁰¹ to X¹⁰⁸ are independently selected from C (including CH) or N. Z¹⁰¹ and Z¹⁰² are independently selected from NR¹⁰¹, O, or S.

Non-limiting examples of the host materials that may be used in an OLED in combination with materials disclosed herein are exemplified below together with references that disclose those materials: EP2034538, EP2034538A, EP2757608, JP2007254297, KR20100079458, KR20120088644, KR20120129733, KR20130115564, TW201329200, US20030175553, US20050238919, US20060280965, US20090017330, US20090030202, US20090167162, US20090302743, US20090309488, US20100012931, US20100084966, US20100187984, US2010187984, US2012075273, US2012126221, US2013009543, US2013105787, US2013175519, US2014001446, US20140183503, US20140225088, US2014034914, U.S. Pat. No. 7,154,114, WO2001039234, WO2004093207, WO2005014551, WO2005089025, WO2006072002, WO2006114966, WO2007063754, WO2008056746, WO2009003898, WO2009021126, WO2009063833, WO2009066778, WO2009066779, WO2009086028, WO2010056066, WO2010107244, WO2011081423, WO2011081431, WO2011086863, WO2012128298, WO2012133644, WO2012133649, WO2013024872, WO2013035275, WO2013081315, WO2013191404, WO2014142472, US20170263869, US20160163995, U.S. Pat. No. 9,466,803,

Additional Emitters:

One or more additional emitter dopants may be used in conjunction with the compound of the present disclosure. Examples of the additional emitter dopants are not particularly limited, and any compounds may be used as long as the compounds are typically used as emitter materials. Examples of suitable emitter materials include, but are not limited to, compounds which can produce emissions via phosphorescence, fluorescence, thermally activated delayed fluorescence, i.e., TADF (also referred to as E-type delayed fluorescence), triplet-triplet annihilation, or combinations of these processes.

Non-limiting examples of the emitter materials that may be used in an OLED in combination with materials disclosed herein are exemplified below together with references that disclose those materials: CN103694277, CN1696137, EB01238981, EP01239526, EP01961743, EP1239526, EP1244155, EP1642951, EP1647554, EP1841834, EP1841834B, EP2062907, EP2730583, JP2012074444, JP2013110263, JP4478555, KR1020090133652, KR20120032054, KR20130043460, TW201332980, U.S. Ser. Nos. 06/699,599, 06/916,554, US20010019782, US20020034656, US20030068526, US20030072964, US20030138657, US20050123788, US20050244673, US2005123791, US2005260449, US20060008670, US20060065890, US20060127696, US20060134459, US20060134462, US20060202194, US20060251923, US20070034863, US20070087321, US20070103060, US20070111026, US20070190359, US20070231600, US2007034863, US2007104979, US2007104980, US2007138437, US2007224450, US2007278936, US20080020237, US20080233410, US20080261076, US20080297033, US200805851, US2008161567, US2008210930, US20090039776, US20090108737, US20090115322, US20090179555, US2009085476, US2009104472, US20100090591, US20100148663, US20100244004, US20100295032, US2010102716, US2010105902, US2010244004, US2010270916, US20110057559, US20110108822, US20110204333, US2011215710, US2011227049, US2011285275, US2012292601, US20130146848, US2013033172, US2013165653, US2013181190, US2013334521, US20140246656, US2014103305, U.S. Pat. Nos. 6,303,238, 6,413,656, 6,653,654, 6,670,645, 6,687,266, 6,835,469, 6,921,915, 7,279,704, 7,332,232, 7,378,162, 7,534,505, 7,675,228, 7,728,137, 7,740,957, 7,759,489, 7,951,947, 8,067,099, 8,592,586, 8,871,361, WO06081973, WO06121811, WO07018067, WO07108362, WO07115970, WO07115981, WO08035571, WO2002015645, WO2003040257, WO2005019373, WO2006056418, WO2008054584, WO2008078800, WO2008096609, WO2008101842, WO2009000673, WO2009050281, WO2009100991, WO2010028151, WO2010054731, WO2010086089, WO2010118029, WO2011044988, WO2011051404, WO2011107491, WO2012020327, WO2012163471, WO2013094620, WO2013107487, WO2013174471, WO2014007565, WO2014008982, WO2014023377, WO2014024131, WO2014031977, WO2014038456, WO2014112450.

HBL:

A hole blocking layer (HBL) may be used to reduce the number of holes and/or excitons that leave the emissive layer. The presence of such a blocking layer in a device may result in substantially higher efficiencies and/or longer lifetime as compared to a similar device lacking a blocking layer. Also, a blocking layer may be used to confine emission to a desired region of an OLED. In some embodiments, the HBL material has a lower HOMO (further from the vacuum level) and/or higher triplet energy than the emitter closest to the HBL interface. In some embodiments, the HBL material has a lower HOMO (further from the vacuum level) and/or higher triplet energy than one or more of the hosts closest to the HBL interface.

In one aspect, compound used in HBL contains the same molecule or the same functional groups used as host described above.

In another aspect, compound used in HBL contains at least one of the following groups in the molecule:

wherein k is an integer from 1 to 20; L¹⁰¹ is an another ligand, k′ is an integer from 1 to 3. ETL:

Electron transport layer (ETL) may include a material capable of transporting electrons. Electron transport layer may be intrinsic (undoped), or doped. Doping may be used to enhance conductivity. Examples of the ETL material are not particularly limited, and any metal complexes or organic compounds may be used as long as they are typically used to transport electrons.

In one aspect, compound used in ETL contains at least one of the following groups in the molecule:

wherein R¹⁰¹ is selected from the group consisting of hydrogen, deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acids, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof, when it is aryl or heteroaryl, it has the similar definition as Ar's mentioned above. Ar¹ to Ar³ has the similar definition as Ar's mentioned above. k is an integer from 1 to 20. X¹⁰¹ to X¹⁰⁸ is selected from C (including CH) or N.

In another aspect, the metal complexes used in ETL contains, but not limit to the following general formula:

wherein (O—N) or (N—N) is a bidentate ligand, having metal coordinated to atoms O, N or N, N; L¹⁰¹ is another ligand; k′ is an integer value from 1 to the maximum number of ligands that may be attached to the metal.

Non-limiting examples of the ETL materials that may be used in an OLED in combination with materials disclosed herein are exemplified below together with references that disclose those materials: CN103508940, EP01602648, EP01734038, EP01956007, JP2004-022334, JP2005149918, JP2005-268199, KR0117693, KR20130108183, US20040036077, US20070104977, US2007018155, US20090101870, US20090115316, US20090140637, US20090179554, US2009218940, US2010108990, US2011156017, US2011210320, US2012193612, US2012214993, US2014014925, US2014014927, US20140284580, U.S. Pat. Nos. 6,656,612, 8,415,031, WO2003060956, WO2007111263, WO2009148269, WO2010067894, WO2010072300, WO2011074770, WO2011105373, WO2013079217, WO2013145667, WO2013180376, WO2014104499, WO2014104535,

Charge Generation Layer (CGL)

In tandem or stacked OLEDs, the CGL plays an essential role in the performance, which is composed of an n-doped layer and a p-doped layer for injection of electrons and holes, respectively. Electrons and holes are supplied from the CGL and electrodes. The consumed electrons and holes in the CGL are refilled by the electrons and holes injected from the cathode and anode, respectively; then, the bipolar currents reach a steady state gradually. Typical CGL materials include n and p conductivity dopants used in the transport layers.

In any above-mentioned compounds used in each layer of the OLED device, the hydrogen atoms can be partially or fully deuterated. Thus, any specifically listed substituent, such as, without limitation, methyl, phenyl, pyridyl, etc. may be undeuterated, partially deuterated, and fully deuterated versions thereof. Similarly, classes of substituents such as, without limitation, alkyl, aryl, cycloalkyl, heteroaryl, etc. also may be undeuterated, partially deuterated, and fully deuterated versions thereof.

EXPERIMENTAL Synthesis of 1,3-bis(1H-benzo[d]imidazol-1-yl)benzene, Ligand L_(A36)

In a 1 L round-bottomed flask 1,3-diiodobenzene (26.43 g, 80 mmol), 1H-benzo[d]imidazole (20.82 g, 176 mmol), and 1,10-phenanthroline (5.77 g, 32.0 mmol), CuI (3.05 g, 16 mmol), and cesium carbonate (120 g, 369 mmol) is combined in anhydrous DMF (350 mL) to give a brown suspension. The reaction is purged with N₂ for 20 minutes and then heated to reflux for 24 hrs. The reaction mixture is passed thought a plug of silica gel (5% MeOH in DCM) to obtain the crude product. The crude product is subjected to silica gel chromatography (400 g, 2% MeOH to 5% MeOH in DCM) to ultimately obtain the final product (12.66 g, 51%).

In a 1 L round bottom flask, compound A (12.66 g, 40.8 mmol), iodomethane (25.5 mL, 408 mmol) were combined in DMF (500 mL) to give a yellow solution. The reaction mixture was heated to 42° C. for 24 hrs and filtered to get the product, ligand L_(A36) (21.69 g, 89%).

Synthesis of 1,3-bis(3H-imidazo[4,5-b]pyridin-3-yl)benzene

A 500 mL round-bottomed flask is charged with 1H-imidazo[4,5-b]pyridine (12.7 g, 107 mmol), 1,3-diiodobenzene (17.65 g, 53.5 mmol), copper (I) oxide (0.176 g, 1.231 mmol), 4,7-dimethoxy-1,10-phenanthroline (0.591 g, 2.46 mmol), cesium carbonate (48.8 g, 150 mmol), polyethylene glycol (9.79 g, D=1.088, 9 mL) and DMSO (125 mL) The reaction mixture is vacuum evacuated and back filled with N₂ three times. The reaction mixture is heated to 110° C. for 24 hours. The reaction mixture was decanted into water (500 mL) and filtered. The precipitate is collected subjected to column chromatography (5% MeOH in DCM) to yield the desired product (6 g, 36%). The reaction with iodomethane as described above provides the corresponding bis(Me-imidazole analog.

The synthesis of the tridentate ligands L_(B) are prepared in a manner similar to the tridentate ligand L_(A) above, and in accordance with the synthetic chemistry described in U.S. Pat. No. 8,754,232, which is assigned to Universal Display Corporation. The corresponding Os(II) and Ru(II) compounds ML_(A)L_(B) are made in accordance with the synthetic processes described in U.S. Pat. No. 7,754,232, assigned to Universal Display Corporation, along with methods known to those of ordinary skill in the art.

TABLE 1 DFT Data of Select Compounds and Comparative Example 1 (CE 1) HOMO LUMO S1 T1 Ex. No. Compound (eV) (eV) (nm) (nm) CE 1

−4.54 −0.85 431 463 2

−4.558 −1.816 601 737 3

−4.472 −1.604 575 664 4

−4.422 −1.479 548 632 5

−4.423 −1.283 520 588 6

−4.463 −1.347 531 604 7

−4.465 −4.465 714 822 8

−4.462 −2.31 857 991 9

−4.581 −2.334 899 1140 *HOMO, LUMO, singlet energy S1, and triplet energy T1 were calculated within the Gaussian16 software package using the B3LYP hybrid functional set and cep-31G basis set. S1 and T1 were obtained using TDDFT at the optimized ground state geometry. A continuum solvent model was applied to simulate tetrahydrofuran solvent.

The DFT data indicates that heteroleptic, bis tridenate Os(II)-carbene compounds, e.g. compounds 2-9, provide an operating design range to extend the light emission of a phosphorescent OLED from about 550 nm to about 1200 nm by simply changing out a tridentate L_(B) ligand. As shown, the light emission can be tuned from green (compound 5 and 6), yellow (compound 3 and 4), red (compound 2) and even reach near IR range (compound 7, 8 and 9).

The calculations obtained with the above-identified DFT functional set and basis set are theoretical. Computational composite protocols, such as the Gaussian09 with B3LYP and CEP-31G protocol used herein, rely on the assumption that electronic effects are additive and, therefore, larger basis sets can be used to extrapolate to the complete basis set (CBS) limit. However, when the goal of a study is to understand variations in HOMO, LUMO, S₁, T₁, bond dissociation energies, etc. over a series of structurally-related compounds, the additive effects are expected to be similar. Accordingly, while absolute errors from using the B3LYP may be significant compared to other computational methods, the relative differences between the HOMO, LUMO, S₁, T₁, and bond dissociation energy values calculated with B3LYP protocol are expected to reproduce experiment quite well. See, e.g., Hong et al., Chem. Mater. 2016, 28, 5791-98, 5792-93 and Supplemental Information (discussing the reliability of DFT calculations in the context of OLED materials). Moreover, with respect to iridium or platinum complexes that are useful in the OLED art, the data obtained from DFT calculations correlates very well to actual experimental data. See Tavasli et al., J. Mater. Chem. 2012, 22, 6419-29, 6422 (Table 3) (showing DFT calculations closely correlating with actual data for a variety of emissive complexes); Morello, G. R., J. Mol. Model. 2017, 23:174 (studying of a variety of DFT functional sets and basis sets and concluding the combination of B3LYP and CEP-31G is particularly accurate for emissive complexes).

It is understood that the various embodiments described herein are by way of example only, and are not intended to limit the scope of the invention. For example, many of the materials and structures described herein may be substituted with other materials and structures without deviating from the spirit of the invention. The present invention as claimed may therefore include variations from the particular examples and preferred embodiments described herein, as will be apparent to one of skill in the art. It is understood that various theories as to why the invention works are not intended to be limiting. 

We claim:
 1. A compound of the formula ML_(A)L_(B); wherein ligand L_(A) is of Formula I, and ligand L_(B) is of Formula II

wherein M is selected from Os(II) or Ru(II), and the compound ML_(A)L_(B) has a formal neutral charge; rings A, B, C, D, E, and F are independently a 5-membered or 6-membered aromatic ring, and R^(A), R^(B), R^(C), R^(D), R^(E), and R^(F) each independently represent mono to the maximum allowable substitution, or no substitution; L¹, L², L³, and L⁴ independently represent a single bond or an organic linking group; W¹, W², W³, and W⁴ are independently selected from carbon or nitrogen; Y¹, Y², Y³, and Y⁴ are independently selected from carbon or nitrogen; Z¹, Z², and Z³ are independently selected from carbon or nitrogen, and at least one of Z¹, Z², and Z³ is nitrogen; wherein each R^(A), R^(B), R^(C), R^(D), R^(E), and R^(F) are independently hydrogen or a substituent selected from the group consisting of deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof, or optionally, any two adjacent substituents of R^(A), R^(B), R^(C), R^(D), R^(E), or R^(F), can join to form a ring.
 2. The compound of claim 1, wherein R^(A), R^(B), R^(C), R^(D), R^(E), and R^(F) are selected from the group consisting of deuterium, fluorine, alkyl, cycloalkyl, heteroalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, aryl, heteroaryl, nitrile, isonitrile, sulfanyl, and combinations thereof.
 3. The compound of claim 1, wherein two of Z¹, Z², and Z³ is nitrogen.
 4. The compound of claim 1, wherein Z¹ is carbon, and ring D is selected from benzene, naphthyl, or an aza-analog of each thereof; each of which is optionally substituted; and Z² and Z³ are nitrogen, or one of Z² and Z³ is nitrogen, and the other is a carbene carbon.
 5. The compound of claim 1, wherein two of rings A, B, and C is an N-heterocyclic carbene ring each with a carbene carbon coordinated to the metal M.
 6. The compound of claim 5, wherein ring A and ring C are the N-heterocyclic carbene rings, and ring B is selected from benzene, naphthyl, or an aza-analog of each thereof; each of which is optionally substituted.
 7. The compound of claim 1, wherein L¹, L², L³, and L⁴ are each a direct bond; each of W¹, W², W³, and W⁴ are carbon, and ring B is an optionally substituted benzene.
 8. The compound of claim 1, wherein L_(A) is selected from the group consisting of:

wherein X¹, X², and X³ are independently selected from C or N; R, R′, R¹, R², and R³ are independently hydrogen or a substituent selected from the group consisting of deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; or optionally, any two adjacent substituents of R¹, R², and R³ can join to form a ring with ring.
 9. The compound of claim 8, wherein each of X¹, X², and X³ is C, and form a benzene ring, which is optionally substituted with R².
 10. The compound of claim 8, wherein two of R¹, two of R², and/or two of R³ join to form a fused benzene ring or an aza-analog thereof; and each fused ring is optionally substituted.
 11. The compound of claim 1, wherein the ligand L_(A) is selected from the group consisting of


12. The compound of claim 1, wherein the ligand L_(B) is selected from the group consisting of

wherein X⁶, X⁷, X⁸, X⁹, X¹⁰, X¹¹, X¹², X¹³, and X¹⁴ are each independently selected from C or N, and each 6-membered aromatic ring has no more than three N; and R″, R⁴, R⁵, and R⁶ are independently hydrogen or a substituent selected from the group consisting of deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; or optionally, any two adjacent substituents of R⁴, R⁵, and R⁶ can join to form a ring with ring.
 13. The compound of claim 12, wherein the ligand L_(B) is selected from the group consisting of

wherein X⁶, X⁷, X⁸, X⁹, X¹⁰, X¹¹, X¹², X¹³, and X¹⁴ are each independently selected from C or N, and each 6-membered aromatic ring has no more than three N; and R″, R⁴, R⁵, and R⁶ are independently hydrogen or a substituent selected from the group consisting of deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; or optionally, any two adjacent substituents of R⁴, R⁵, and R⁶ can join to form a ring with ring.
 14. The compound of claim 1, wherein the ligand L_(B) is selected from the group consisting of


15. The compound of claim 14, wherein the compound is the Compound x having the formula M(L_(Ai))(L_(Bj)); wherein x=151i+j−151; i is an integer from 1 to 68; and j is an integer from 1 to 151; and wherein L_(Ai) has the following structure:


16. An organic light emitting device (OLED) comprising an anode, a cathode, and an organic layer disposed between the anode and the cathode, the organic layer comprising a compound of the formula ML_(A)L_(B); wherein ligand L_(A) is of Formula I, and ligand L_(B) is of Formula II

wherein M is selected from Os(II) or Ru(II), and the compound ML_(A)L_(B) has a formal neutral charge; rings A, B, C, D, E, and F are independently a 5-membered or 6-membered aromatic ring, and R^(A), R^(B), R^(C), R^(D), R^(E), and R^(F) each independently represent mono to the maximum allowable substitution, or no substitution; L¹, L², L³, and L⁴ independently represent a single bond or an organic linking group; W¹, W², W³, and W⁴ are independently selected from carbon or nitrogen; Y¹, Y², Y³, and Y⁴ are independently selected from carbon or nitrogen; Z¹, Z², and Z³ are independently selected from carbon or nitrogen, and at least one of Z¹, Z², and Z³ is nitrogen; wherein each R^(A), R^(B), R^(C), R^(D), R^(E), and R^(F) are independently hydrogen or a substituent selected from the group consisting of deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof, or optionally, any two adjacent substituents of R^(A), R^(B), R^(C), R^(D), R^(E), or R^(F), can join to form a ring.
 17. The OLED of claim 16, wherein the organic layer further comprises a host, wherein the host comprises at least one chemical group selected from the group consisting of triphenylene, carbazole, dibenzothiophene, dibenzofuran, dibenzoselenophene, azatriphenylene, azacarbazole, aza-dibenzothiophene, aza-dibenzofuran, and aza-dibenzoselenophene.
 18. The OLED of claim 16, wherein the organic layer provides light emission in a range selected from the group consisting of: from 700 nm to 1200 nm, from 800 nm to 1200 nm, from 900 nm to 1200 nm, and from 1000 nm to 1200 nm.
 19. A consumer product comprising an organic light-emitting device (OLED) comprising: an anode, a cathode, and an organic layer disposed between the anode and the cathode, the organic layer comprising a compound of the formula ML_(A)L_(B); wherein ligand L_(A) is of Formula I, and ligand L_(B) is of Formula II

wherein M is selected from Os(II) or Ru(II), and the compound ML_(A)L_(B) has a formal neutral charge; rings A, B, C, D, E, and F are independently a 5-membered or 6-membered aromatic ring, and R^(A), R^(B), R^(C), R^(D), R^(E), and R^(F) each independently represent mono to the maximum allowable substitution, or no substitution; L¹, L², L³, and L⁴ independently represent a single bond or an organic linking group; W¹, W², W³, and W⁴ are independently selected from carbon or nitrogen; Y¹, Y², Y³, and Y⁴ are independently selected from carbon or nitrogen; Z¹, Z², and Z³ are independently selected from carbon or nitrogen, and at least one of Z¹, Z², and Z³ is nitrogen; wherein each R^(A), R^(B), R^(C), R^(D), R^(E), and R^(F) are independently hydrogen or a substituent selected from the group consisting of deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof, or optionally, any two adjacent substituents of R^(A), R^(B), R^(C), R^(D), R^(E), or R^(F), can join to form a ring; wherein the consumer product is selected from the group consisting of a flat panel display, a computer monitor, a medical monitor, a television, a billboard, a light for interior or exterior illumination and/or signaling, a heads-up display, a fully or partially transparent display, a flexible display, a laser printer, a telephone, a cell phone, tablet, a phablet, a personal digital assistant (PDA), a wearable device, a laptop computer, a digital camera, a camcorder, a viewfinder, a micro-display that is less than 2 inches diagonal, a 3-D display, a virtual reality or augmented reality display, a vehicle, a video wall comprising multiple displays tiled together, a theater or stadium screen, a light therapy device, and a sign.
 20. A formulation comprising a compound in accordance with claim
 1. 